Signal transfer device and signal transfer method

ABSTRACT

A buffer unit including a plurality of buffers, a sorting unit configured to sort an input signal to any of the plurality of buffers based on header information, a rate calculation unit configured to calculate a rate at which the input signal is read from each of the plurality of buffers based on burst information of the input signal, an adjustment unit configured to adjust a rate at which the input signal is read from each of the plurality of buffers based on the rate calculated by the rate calculation unit, and a transfer unit configured to transfer the signal read from each of the plurality of buffers are provided.

TECHNICAL FIELD

The present invention relates to a signal transfer device and a signaltransfer method.

BACKGROUND ART

Examples of networks constituting a cellular system include mobilefronthaul (MFH), mobile backhaul (MBH), and the like.

MBH is a network between a base station and an aggregate station thatcontrols the base station, and is constructed with a layer-2 switch, arouter, and the like.

On the other hand, MFH is a configuration between a radio control deviceand a radio device in a configuration in which a base station isdeployed separately from the radio control device and the radio device.Although a point-to-point connection is employed in this section in therelated art, a network built with a passive optical network (PON) (seePatent Literature 1) or with a configuration in which layer-2 switchesare connected in multiple layers (see Non Patent Literature 1) has beendiscussed, which can achieve efficient accommodation compared to apoint-to-point connection.

CITATION LIST Patent Literature

Patent Literature 1: JP 5876941 B

Non Patent Literature

Non Patent Literature 1: “IEEE Standard for Local and Metropolitan AreaNetworks-Time-Sensitive Networking for Fronthaul,” IEEE StandardsAssociation, 7 May 2018

SUMMARY OF THE INVENTION Technical Problem

However, in a signal transfer device such as a layer-2 switch or arouter deployed between a radio device and a radio control device of therelated art, sufficient statistical multiplexing effects may not beobtained because signals are increasingly discarded due to a trafficconcentration, or the like.

An object of the present invention is to provide a signal transferdevice and a signal transfer method capable of increasing the number ofmultiplexed signals while reducing discarded signals.

Means for Solving the Problem

A signal transfer device according to an aspect of the present inventionincludes a buffer unit including a plurality of buffers, a sorting unitconfigured to sort an input signal to any of the plurality of buffersbased on header information, a rate calculation unit configured tocalculate a rate at which the input signal is read from each of theplurality of buffers based on burst information of the input signal, anadjustment unit configured to adjust a rate at which the input signal isread from each of the plurality of buffers based on the rate calculatedby the rate calculation unit, and a transfer unit configured to transferthe signal read from each of the plurality of buffers.

In addition, a signal transfer method according to an aspect of thepresent invention includes sorting an input signal to any of a pluralityof buffers based on header information, calculating a rate at which theinput signal is read from each of the plurality of buffers based onburst information of the input signal, adjusting a rate at which theinput signal is read from each of the plurality of buffers based on thecalculated rate, and transferring the signal read from each of theplurality of buffers.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a first configuration example of asignal transfer device that uses burst information.

FIG. 2(a) is a diagram illustrating a first operation example in whichsignal intervals in burst periods are equally spaced. FIG. 2(b) is adiagram illustrating a second operation example in which signalintervals in burst periods are equally spaced. FIG. 2(c) is a diagramillustrating a third operation example in which signal intervals inburst periods are equally spaced.

FIG. 3 is a diagram illustrating an example of an operation of a radiocommunication system in which signal transfer devices are replaced onlywith signal transfer devices operating as in the first operationexample.

FIG. 4 is a diagram illustrating a second configuration example of thesignal transfer device that uses burst information.

FIG. 5 is a diagram illustrating an example of a configuration of aradio communication system.

FIG. 6 is a diagram illustrating an example of a configuration of asignal transfer device.

FIG. 7 is a diagram illustrating an example of an operation of the radiocommunication system.

FIG. 8 is a diagram illustrating an example of an operation in which theradio communication system performs shaping.

DESCRIPTION OF EMBODIMENTS

First, the background to the present invention will be described. Here,although a signal transfer device and a signal transfer method will bedescribed using MFH as an example, the signal transfer device and thesignal transfer method may be applied to MBH with a radio device read asa base station and with a radio control device read as an aggregatestation. In addition, layer 2 switches, routers, and the like all willbe assumed as signal transfer devices without distinguishing them fromeach other.

For example, as a network configured of a plurality of signal transferdevices, some accommodate communication between a plurality of radiodevices and radio control devices. First, merging of communication in aradio communication system equipped with such a network will bedescribed.

FIG. 5 is a diagram illustrating an example of a configuration of aradio communication system 1. The radio communication system 1 includes,for example, four radio devices 2-1 to 2-4 and one radio control device3 that controls the radio devices 2-1 to 2-4. Further, in the radiocommunication system 1, signal transfer devices 4-1 to 4-5 are providedbetween the radio devices 2-1 to 2-4 and the radio control device 3.

For example, the signal transfer devices 4-1 to 4-4 receive signalstransmitted by the radio devices 2-1 to 2-4, respectively, and transferthe signals to the signal transfer device 4-5. The signal transferdevice 4-5 transfers the signals received from the signal transferdevices 4-1 to 4-4 to the radio control device 3. In a case in which aplurality of constituent components, such as the signal transfer devices4-1 to 4-5, do not need to be distinguished from each other, theconstituent components will be simply referred to as signal transferdevices 4, or the like.

FIG. 6 is a diagram illustrating an example of a configuration of eachsignal transfer device 4. As illustrated in FIG. 6, the signal transferdevice 4 includes a sorting unit 40, a buffer unit 41, an adjustmentunit 42, and a transfer unit 43.

The sorting unit 40 sorts input signals to any of buffers 410-1 to410-n, which will be described below, based on header information.

The buffer unit 41 b includes, for example, n buffers 410-1 to 410-n,and the buffers 410-1 to 410-n hold (store) the signals sorted by thesorting unit 40.

The adjustment unit 42 adjusts each rate at which the buffers 410-1 to410-n read the held signals.

The transfer unit 43 reads the signals held in the buffers 410-1 to410-n at the reading rates adjusted by the adjustment unit 42 andtransfers the read signals.

In the radio communication system 1 illustrated in FIG. 5, signals inthe uplink communication traffic output by the signal transfer devices4-1 to 4-4 are merged at the signal transfer device 4-5. For the sake ofsimple explanation, it is assumed that interfaces included in the signaltransfer devices 4-1 to 4-5 have a maximum transmission rate of 10 Gbps.That is, if a rate of total traffic flowing from the radio devices 2-1to 2-4 is 10 Gbps or lower, the signal transfer device 4-5 canaccommodate all signals on one interface.

On the other hand, traffic flowing through a mobile network has burstproperties. FIG. 7 is a diagram illustrating an example of an operationof the radio communication system 1 with the burst properties. Asillustrated in FIG. 7, in communication with the burst properties,signals are instantaneously transmitted at a maximum interfacetransmission rate.

Thus, in a case in which a plurality of signals merge at a point likethe signal transfer device 4-5, it is likely that an input transmissionrate of the signal transfer device 4-5 will instantaneously exceedoutput transmission rates of the individual signal transfer devices 4-1to 4-4.

At this time, if the signal transfer device 4-5 does not have asufficient quantity of buffers, buffer overflow occurs, and frames arelost (signals are discarded). In the example illustrated in FIG. 7,signals are instantaneously input at a total rate of 40 Gbps to theinterface with the maximum transmission rate of 10 Gbps due to mergingof the signals, which causes the signals to be discarded. In addition,although the signal transfer device 4-5 may be configured to have asufficient quantity of buffers to prevent buffer overflow, the circuitscale may increase in that case.

Thus, the radio communication system 1 may reduce discarded signalsthrough shaping. Shaping is an operation in which a maximum outputtransmission rate, which is equal to or below a maximum transmissionrate of an interface, is determined, and in a case in which an inputtraffic rate instantaneously exceeds the maximum output transmissionrate, frames are accumulated and delayed and the output transmissionrate is dropped to a predetermined rate.

FIG. 8 is a diagram illustrating an example of an operation in which theradio communication system 1 performs shaping. As illustrated in FIG. 8,in the radio communication system 1, the signal transfer devices 4-1 to4-4 may drop a signal transmission rate by performing shaping beforetransferring signals to the signal transfer device 4-5.

Here, each of the signal transfer devices 4-1 to 4-4 includes aninterface with a transmission rate of 10 Gbps, and delays a signal usingthe buffer unit 41 to keep an output transmission rate lower than orequal to 3 Gbps. In other words, each of the signal transfer devices 4-1to 4-4 has the adjustment unit 42 to keep a maximum average transmissionrate at 3 Gbps within one burst period.

In a case in which the amount of traffic from the radio devices 2-1 to2-4 is transferred at a higher rate than that of the signal transferdevices 4-1 to 4-4, signals in a burst period will be transmitted acrossthe next burst period. When this state continues, the signal transferdevices 4-1 to 4-4 continue to accumulate frames in the buffer units 41,causing buffer overflow.

Thus, when each of the radio devices 2-1 to 2-4 outputs a signal at 3Gbps, the signal transfer devices 4-1 to 4-4 need to set the outputtransmission rate from the buffer unit 41 to a minimum of 3 Gbps usingthe adjustment unit 42.

In this case, if the output transmission rate at the beginning of theburst period becomes 3 Gbps and the amount of traffic is low, there is asection in which no frame flows later in the burst period as illustratedin FIG. 8.

If such signals are transferred from the signal transfer devices 4-1 to4-4 to the signal transfer device 4-5 at the same time, signals areinstantaneously input to the signal transfer device 4-5 at 12 Gbps. Atthis time, because the signals are input (at 12 Gps) in excess of themaximum transmission rate (10 Gbps), the signal transfer device 4-5 canhave frame loss reduced more than the example illustrated in FIG. 7, butif a sufficient quantity of buffers is not provided, buffer overflowoccurs, resulting in frame loss.

If a sufficient quantity of buffers is provided to prevent bufferoverflow, the circuit scale of the signal transfer devices increases. Inaddition, if transmission rates of traffic flowing from the signaltransfer devices 4-1 to 4-4 vary, the signal transfer device 4-5 canefficiently accommodate the traffic taking advantage of statisticalmultiplexing effects. However, a transmission rate at the beginning of aburst period should be fixed (at 3 Gbps)in the related art, andtherefore, it is not possible to perform accommodation taking advantageof the statistical multiplexing effects.

Also, as a solution that prevents buffer overflow, a method isconceivable in which signals from the signal transfer devices 4-1 to 4-4to the signal transfer device 4-5 are controlled such that the they donot reach at the same time. However, in such a method, it is necessaryto examine arrival timings of frames coming from each of the signaltransfer devices deployed in the preceding stage at each signal transferdevice on the network, and to control output timings of the frames ateach signal transfer device, which complicates operations of the systemor a user.

Next, a signal transfer device that transfers a signal (a frame or thelike) using burst information will be described.

FIG. 1 is a diagram illustrating a first configuration example (signaltransfer device 4 a) of a signal transfer device that transfers a signalusing burst information. The signal transfer device 4 a replaces each ofthe signal transfer devices 4-1 to 4-5 in the radio communication system1 illustrated in FIG. 5, for example, to constitute a radiocommunication system.

For example, four signal transfer devices 4 a receive signalstransmitted by the radio devices 2-1 to 2-4, and transfer the signals toanother signal transfer device 4 a. The other signal transfer device 4 atransfers the signals received from each of the four signal transferdevices 4 a to a radio control device 3.

Each signal transfer device 4 a includes a sorting unit 40, a bufferunit 41, a transfer unit 43, a burst information acquisition unit 44, arate calculation unit 45, and an adjustment unit 46 as illustrated inFIG. 1. Further, the same reference numerals are given to constituentcomponents of the signal transfer device 4 a illustrated in FIG. 1 thatare substantially the same as those of the signal transfer device 4illustrated in FIG. 6.

The burst information acquisition unit 44 acquires burst informationfrom the outside and outputs the acquired burst information to the ratecalculation unit 45. The burst information includes, for example, atleast any of a total frame length and a burst length within the burst,as well as a burst period.

The rate calculation unit 45 calculates a rate at which an input signalis read from each of buffers 410-1 to 410-n based on the burstinformation acquired by the burst information acquisition unit 44 andoutputs the calculated rate to the adjustment unit 46. For example, therate calculation unit 45 calculates a rate at which an input signal isread from the buffers 410-1 to 410-n so that signal (frame) intervalsare equally spaced in the burst period.

The adjustment unit 46 adjusts the rate at which the input signal isread from each of the buffers 410-1 to 410-n based on the ratecalculated by the rate calculation unit 45. For example, the adjustmentunit 46 adjusts the rate at which the signal is read from the buffers410-1 to 410-n in each burst period so that the signal (frame) intervalsare equally spaced in the burst period.

FIG. 2 includes diagrams illustrating operation examples in which thesignal transfer device 4 a sets signal (frame) intervals in burstperiods to be equally spaced for each burst period. FIG. 2(a) is adiagram illustrating a first operation example in which signal intervalsin burst periods are equally spaced. FIG. 2(b) is a diagram illustratinga second operation example in which signal intervals in burst periodsare equally spaced. FIG. 2(c) is a diagram illustrating a thirdoperation example in which signal intervals in burst periods are equallyspaced. Further, the burst signals illustrated at the top are a signalin an i-th burst period input to the signal transfer device 4 a (asignal before rate adjustment) and a signal in an (i+1)-th burst period.

In the first operation example illustrated in FIG. 2(a), the signaltransfer device 4 a starts outputting first frames (#1 and #5) in theburst periods at the same time as a burst start time, similarly to theinput signal (the signal before rate adjustment). At this time, thesignal transfer device 4 a makes the time interval between the lastframe (#4) in the burst period and the previous frame (#3) the same asthe time interval between the last frame (#4) and the next burst starttime (the first frame (#5) in the next burst period).

In the second operation example illustrated in FIG. 2(b), the signaltransfer device 4 a finishes the output of the last frame (#4) in theburst period at the same time as the end time of the burst period. Inaddition, the signal transfer device 4 a makes the time interval betweenthe first frame (#5) in the burst period and the next frame (#6) thesame as the time interval between the first frame (#5) and the last timein the previous burst period (the last frame (#4) in the one burstperiod before).

In the second operation example illustrated in FIG. 2(b), a delay timeof each frame increases compared to the first operation exampleillustrated in FIG. 2(a). However, the signal transfer devices 4-1 to4-4 in the radio communication system 1 (FIG. 5) may be replaced with aconfiguration in which the signal transfer device 4 a that operates asin the first operation example and the signal transfer device 4 a thatoperates as in the second operation example are combined.

In this case, the number of frames arriving at the signal transferdevice 4-5 at the same time can be further reduced compared to a case inwhich all of the signal transfer devices 4-1 to 4-4 in the radiocommunication system 1 are replaced only with the signal transfer device4 a that operates as in the first operation example, or only with thesignal transfer device 4 a that operates as in the second operationexample. That is, there is a possibility of further reducing a quantityof buffers of the signal transfer device 4-5.

The first operation example and the second operation example illustratedin FIGS. 2(a) and 2(b) are realized, for example, by the burstinformation acquisition unit 44 of the signal transfer device 4 a(FIG. 1) obtaining burst information in advance from an external radiodevice 2, the radio control device 3, or the like.

However, in the first operation example and the second operationexample, the rate of reading from the buffer 410 to be adjusted by theadjustment unit 46 should be calculated by the rate calculation unit 45at the start time of the burst period or after a very small period oftime elapses from the start of the burst period.

In the third operation example illustrated in FIG. 2(c), the signaltransfer device 4 a performs the same operation as the first operationexample illustrated in FIG. 2(a) after one burst period is delayed. Inthis case, the signal transfer device 4 a may calculate the interval ofsignals to be output in the (i+1)-th burst period during the i-th burstperiod.

FIG. 3 is a diagram illustrating an operation example of the radiocommunication system 1 in which all of the signal transfer devices 4-1to 4-4 are replaced only with the signal transfer device 4 a thatoperates as in the first operation example illustrated in FIG. 2(a).

In the radio communication system 1 in which the signal transfer devicesare replaced only with the signal transfer device 4 a that operates asin the first operation example, four signal transfer devices 4 a outputframes output by the respective radio devices 2-1 to 2-4 at equal timeintervals in each burst period as illustrated in FIG. 3.

For example, in the i-th burst period, the four signal transfer devices4 a set a rate of a signal output by the radio device 2-1 to 2.4 Gbps, arate of a signal output by the radio device 2-2 to 1.2 Gbps, and a rateof signals output by the radio devices 2-3 and 2-4 to 1.8 Gbps,respectively. At this time, the signals input from the four signaltransfer devices 4 a to the signal transfer device 4-5 have a total rateof 7.2 Gbps.

In addition, in the (i+1)-th burst period, the four signal transferdevices 4 a set a rate of signals output by the radio devices 2-1 and2-2 to 1.8 Gbps, a rate of a signal output by the radio device 2-3 to 3Gbps, and a rate of a signal output by the radio device 2-4 to 1.2 Gbps,respectively. At this time, the signals input from the four signaltransfer devices 4 a to the signal transfer device 4-5 have a total rateof 7.8 Gbps.

Although the total output rate instantaneously reaches 12 Gbps when thesignal transfer devices 4-1 to 4-4 perform shaping to set 3 Gbps as alimit rate (see FIG. 8) in the radio communication system 1 as describedabove, the total output rate does not exceed 10 Gbps when the signaltransfer devices are replaced with the four signal transfer devices 4 a(FIG. 3).

In other words, the transmission rate of the signals input to the signaltransfer device 4-5 is minimized in any of the burst periods, and it islower than or equal to the maximum transmission rate of the interface(10 Gbps), which prevents frame loss. When the transmission rate of thesignals input to the signal transfer device 4-5 is minimized, the radiocommunication system 1 is likely to accommodate traffic from a newsignal transfer device, taking advantage of the statistical multiplexingeffects.

FIG. 4 is a diagram illustrating a second configuration example (signaltransfer device 4 b) of the signal transfer device that transfers asignal using burst information. The signal transfer device 4 b replaceseach of the signal transfer devices 4-1 to 4-5 in the radiocommunication system 1 illustrated in FIG. 5, for example, to constitutethe radio communication system.

For example, four signal transfer devices 4 b receive signalstransmitted by the radio devices 2-1 to 2-4 and transfer the signals toanother signal transfer device 4 b. The other signal transfer device 4 btransfers the signals received from each of the four signal transferdevices 4 b to the radio control device 3.

As illustrated in FIG. 4, the signal transfer device 4 b includes asorting unit 40, a buffer unit 41 b, a transfer unit 43, a ratecalculation unit 45, an adjustment unit 46, and a burst informationcalculation unit 47. Further, the same reference numerals are given tosubstantially the same constituent components of the signal transferdevice 4 b illustrated in FIG. 4 as those of the signal transfer device4 a illustrated in FIG. 1.

The buffer unit 41 b includes, for example, n buffers 410-1 to 410-n,and the buffers 410-1 to 410-n hold (store) the signals sorted by thesorting unit 40. In addition, the buffer unit 41 b outputs the signalsheld by the buffers 410-1 to 410-n to the burst information calculationunit 47.

The burst information calculation unit 47 calculates burst informationfrom the signals input from the buffer unit 41 b, and outputs thecalculated burst information to the rate calculation unit 45. Then, therate calculation unit 45 calculates a rate at which the input signalsare read from each of the buffers 410-1 to 410-n based on the burstinformation calculated by the burst information calculation unit 47 andoutputs the calculated rates to the adjustment unit 46.

For example, the rate calculation unit 45 calculates the rate at whichframes are read from each of the buffers 410-1 to 410-n at an i-th burstillustrated in FIG. 2(c) until the i-th burst period ends based on theburst information calculated by the burst information calculation unit47.

Then, the buffer unit 41 b transmits the frames of the i-th burst in the(i+1)-th burst period (FIG. 2(c)). In other words, the signal transferdevice 4 b has a longer frame delay than the signal transfer device 4 athat operates as in the first operation example and the second operationexample illustrated in FIGS. 2(a) and 2(b). However, because the signaltransfer device 4 b calculates the burst information from the framesheld in the buffer unit 41 b, it is not necessary to acquire burstinformation from the outside.

Further, when the read rate for the i-th burst is adjusted, the signaltransfer device 4 b may predict and calculate the i-th burst informationbased on the zero-th to (i−1)-th burst information. In this case, thesignal transfer device 4 b can implement the operations of the firstoperation example and the second operation example illustrated in FIGS.2(a) and 2(b).

In addition, the signal transfer device 4 b may further include theburst information acquisition unit 44 illustrated in FIG. 1. In otherwords, in a case in which the burst information calculation unit 47 andthe burst information acquisition unit 44 are included, the signaltransfer device 4 b may acquire the burst information that is obtainedfrom the outside using the burst information acquisition unit 44, andmay calculate the burst information that is not obtained from theoutside using the burst information calculation unit 47. Furthermore,the signal transfer device 4 b may perform calculation to correct theburst information using the burst information calculation unit 47 whileacquiring the burst information using the burst information acquisitionunit 44.

Hereinafter, processing using burst information will be described indetail with, as an example, a case in which the signal transfer device 4b further includes the burst information acquisition unit 44 illustratedin FIG. 1.

For the processing using burst information, for example, a burst periodis set as T[s], the number of frames in the i-th burst as a frame lengthof a j-th frame in the i-th burst as p_(i,j) [byte] (n_(i)≥j≥1), aninterval between the j-th and (j+1)-th frames as a_(i,j) [byte](n_(i)−1≥j≥1), and a transmission rate of the interface of the signaltransfer device 4 b as r [bit/sec].

A burst length B_(i)[s] of the i-th burst (where i is an integer equalto or greater than 1) is B_(i)=8(Σ(j=1:n_(i))p_(i,j)+Σ(j=1:n_(i-1))a_(i,j))/r.

A plurality of patterns such as, for example, (1) to (3) below areconceivable for the specific operation performed by the signal transferdevice 4 b.

(1) To equally space frames in the burst period, the rate calculationunit 45 calculates t₁=(T−Σ(j=1:n_(i))p_(i,j)/r)/n. Then, the adjustmentunit 46 adjusts each frame spacing to L. In this case, the burstinformation acquisition unit 44 needs to obtain information on the burstperiod T, a total frame length Σ(=1:n_(i))p_(i,j) in the burst, and thenumber of frames n_(i) in the burst.

(2) If the signal is an Ethernet frame, the frame spacing is at least 12bytes. At this time, the frame spacing in the burst is thought to be avalue close to this value (12 bytes). Thus, if the frame spacings of theinput signals in the burst are all the same and all a_(i,j) are equal toa [byte] in the range (n−1≥j≥1), the rate calculation unit 45 calculatest₂=(T−B_(i)+8(n−1)a/r)/n in order to equally space frames in the burst.Then, the adjustment unit 46 adjusts each frame spacing to t₂. In thiscase, the burst information acquisition unit 44 needs to obtaininformation on the burst period T, the burst length B, and the number offrames n_(i) in the burst.

(3) If the signal is an Ethernet frame, the frame length is 1518 bytesat the longest. At this time, a frame length in the burst is thought tobe a value close to this value (1518 bytes). Thus, the burst informationcalculation unit 47 estimates the number of frames asn_(i)=(rB_(i)/8+a)/(a+b) if all of the burst spacings in the burst arethe same, the frame lengths in the burst are equal, and all p_(i,j) areequal to b [bytes] in the range of (n_(i)≥j≥1). Thus, the ratecalculation unit 45 calculatest₃=(T−B_(i)+8(n−1)a/r)/((rB_(i)/8+a)/(a+b)) in order to equally spacethe frames in the burst. Then, the adjustment unit 46 adjusts each framespacing to t₃. In this case, the burst information acquisition unit 44needs to obtain information on the burst period T and the burst lengthB. Although a frame length of the frame flowing at the end of the burstis not likely to be b due to the adjustment, if the number of framesn_(i) is sufficiently large, the effect of the adjustment is thought tobe negligible.

Next, a method of acquiring, by the burst information acquisition unit44, burst information will be described in detail. The burst informationacquisition unit 44 acquires burst information from the external radiodevice 2, the radio control device 3 (FIG. 5), or the like.

For example, in a case in which the radio communication system 1 is aLong Term Evolution (LTE) system, scheduling is performed in the MAClayer at intervals of 1 ms and communication is performed between theradio device 2 and the radio control device 3 based on the schedulingresults.

Thus, when the burst information acquisition unit 44 checks thescheduling information, it is thought that a burst period T in the burstof traffic flowing in the signal transfer device 4 b, a total framelength Σ(=1:n_(i))p_(i,j), a burst length B, the number of frames andthe like can be acquired.

In addition, although scheduling is performed in the MAC layer at theintervals of 1 ms, and the interval of 1 ms is constituted by 14 OFDMsymbols, and thus, it is thought that a burst period is determined witha layer deployed in the radio device 2 and the radio control device 3,that is, a function division point.

In other words, in a case in which a function division point is set nearthe MAC layer, traffic flowing in the signal transfer device 4 b isassumed to have burst signals at intervals close to the interval of 1ms. However, in a case in which a function division point is set nearthe lower PHY layer in an FFT/IFFT, or the like, an interval ofapproximately an Orthogonal Frequency Division Multiplexing (OFDM)symbol is assumed.

Further, although the case in which the burst information acquisitionunit 44 acquires the burst information from the MAC layer has beendescribed in the example described above, the burst informationacquisition unit 44 may acquire burst information from another layer.

Next, a method of calculating, by the burst information calculation unit47, burst information will be described in detail. Because burst signalsexist in the frame at the beginning of the burst period at all times, aburst period T can be estimated if the time at which the head frame hasbeen detected is confirmed and the interval is calculated.

In a case of bursts, the spacing between the first frame and the nextframe in a burst is very short, but the spacing between the first framein the burst and the last frame in the previous burst is relativelylong. For this reason, it is easy to estimate which frame is the head ifthe latter spacing is compared.

The burst information calculation unit 47 can calculate a total framelength Σ(j=1:n_(i))p_(i,j) in a burst by checking a quantity of dataheld in the buffer unit 41 b.

In addition, the burst information calculation unit 47 can check thetime at which the first frame in the burst period has arrived and thetime at which the last frame in the burst period has arrived, andcalculate a burst length B_(i) using the spacing.

Furthermore, the burst information calculation unit 47 can determinewhich frame is the last frame of the burst period based on whether thetime in which no other frames are received exceeds a certain valuebecause no other frame is received for a while after the last frame ofthe burst period is received.

In addition, the signal transfer device 4 b may be configured such thata frame counter that counts the number of frames is provided in thesorting unit 40 to calculate the number of frames The number of framesn_(i) may be estimated to be n_(i)=(rB_(i)/8+a)/(a+b) as describedabove.

As described above, the signal transfer device 4 a and the signaltransfer device 4 b can increase the number of multiplexed signalsbecause an instantaneous transmission rate is minimized in the burstperiod by adjusting the output transmission rate for each burst to havethe signals (frames) equally spaced in the burst period based on theburst information. In addition, the signal transfer device 4 a and thesignal transfer device 4 b can easily obtain the statisticalmultiplexing effects and increase the number of multiplexed signalsbecause they can have instantaneous transmission rates varying inaccordance with the burst length (amount of traffic).

Further, the above-described signal transfer device 4 a and the signaltransfer device 4 b are not limited to being used in the radiocommunication system 1 provided with the radio device 2 and the radiocontrol device 3 and are applicable to another radio communicationsystem as well.

For example, the signal transfer device 4 a and the signal transferdevice 4 b are applicable as signal transfer devices that accommodate anF1 interface between a radio device and a radio control device even in aconfiguration in which only a packet data convergence protocol (PDCP)layer is deployed for the radio control device and radio link control(RLC) and lower layers are deployed in the radio device.

In addition, the signal transfer device 4 a and the signal transferdevice 4 b are applicable as signal transfer devices that accommodate acommon public radio interface (eCPRI) interface between a radio deviceand a radio control device even in a configuration in which only a partof the PHY layer is deployed in the radio device and the higher layersare deployed in the radio control device.

In addition, the signal transfer device 4 a and the signal transferdevice 4 b are also applicable to any networks of a ring type, a meshtype, a honeycomb type, and the like.

Further, some or all of the units constituting the signal transferdevice 4 a and the signal transfer device 4 b described above may beconfigured by hardware, or may be configured by executing a program on aprocessor.

In addition, in a case in which some or all of the units constitutingthe signal transfer device 4 a and the signal transfer device 4 b areconfigured by causing the processor to execute a program, the programmay be recorded in a recording medium and supplied, or may be suppliedvia a network.

REFERENCE SIGNS LIST

1 Radio communication system

2-1 to 2-4 Radio device

3 Radio control device, signal transfer device

4-1 to 4-5, 4 a, 4 b Signal transfer device

40 Sorting unit

41, 41 b Buffer unit

43 Transfer unit

44 Burst information acquisition unit

45 Rate calculation unit

46 Adjustment unit

47 Burst information calculation unit

410-1 to 410-n Buffer

1. A signal transfer device comprising: a buffer unit including aplurality of buffers; a sorting unit configured to sort an input signalto any of the plurality of buffers based on header information; a ratecalculation unit configured to calculate a rate at which the inputsignal is read from each of the plurality of buffers based on burstinformation of the input signal; an adjustment unit configured to adjusta rate at which the input signal is read from each of the plurality ofbuffers based on the rate calculated by the rate calculation unit; and atransfer unit configured to transfer the signal read from each of theplurality of buffers.
 2. The signal transfer device according to claim1, further comprising: a burst information acquisition unit configuredto acquire the burst information from an outside, wherein the ratecalculation unit calculates the rate at which the input signal is readfrom each of the plurality of buffers based on the burst informationacquired by the burst information acquisition unit.
 3. The signaltransfer device according to claim 1, further comprising: a burstinformation calculation unit configured to calculate the burstinformation based on the input signal, wherein the rate calculation unitcalculates the rate at which the input signal is read from each of theplurality of buffers based on the burst information calculated by theburst information calculation unit.
 4. The signal transfer deviceaccording to claim 1, wherein the burst information includes at leastone of a total frame length in a burst or a burst length, and a burstperiod, and the rate calculation unit calculates the rate at which theinput signal is read from each of the plurality of buffers so thatsignal intervals are equally spaced in the burst period.
 5. A signaltransfer method comprising: sorting an input signal to any of aplurality of buffers based on header information; calculating a rate atwhich the input signal is read from each of the plurality of buffersbased on burst information of the input signal; adjusting a rate atwhich the input signal is read from each of the plurality of buffersbased on the calculated rate; and transferring the signal read from eachof the plurality of buffers.
 6. The signal transfer method according toclaim 5, further comprising: acquiring the burst information from anoutside, wherein the calculating of the rate includes calculating therate at which the input signal is read from each of the plurality ofbuffers based on the burst information acquired in the acquiring of theburst information.
 7. The signal transfer method according to claim 5,further comprising: calculating the burst information using the inputsignal, wherein the calculating of the rate includes calculating therate at which the input signal is read from each of the plurality ofbuffers based on the burst information calculated in the calculating ofthe burst information.
 8. The signal transfer method according to claim5, wherein the burst information includes at least one of a total framelength in a burst or a burst length, and a burst period, and thecalculating of the rate includes calculating the rate at which the inputsignal is read from each of the plurality of buffers so that signalintervals are equally spaced in the burst period.